Synapses are the major locus of information transfer within our brain as well as the target of numerous pathologies which can afflict humans from development in utero to death. Therefore, major research effort is given to understanding synapse formation and stabilization throughout life. The scientific literature concerning synapses is rich with discovery of fundamental principles derived from study of the neuromuscular junction (NMJ). In particular, proteins responsible for NMJ function, formation, and stability are relatively well understood. Nevertheless, fundamental questions remain concerning interactions between these proteins. An important experimental model suggests that heterogeneous activity of AChRs influences stability of the adult NMJ. This proposal modifies and extends that model to the developing NMJ where co-expression of immature gamma and mature epsilon AChRs during the critical phase of NMJ maturation produces heterogeneity of end-plate activity. Our model suggests that end-plate areas rich in epsilon AChR mediate Ca 2+ influx which activates co-localized nitric oxide synthase (nNOS). The nitric oxide (NO) produced diffuses to nerve terminals competing for the motor end-plate. New preliminary data suggest that NO enhances Ca2+ currents and transmitter release at adult motor nerve terminals. Thus, developing nerve terminals activating end-plate loci containing the epsilon AChR may be functionally enhanced and nurtured via NO activation of presynaptic guanylyl cyclase. In contrast, NO may repress function and stability of competing nerve terminals activating epsilon AChR poor end-plate foci. The mouse Triangularis sterni (TS) preparation facilitates exact testing of our model. Our preliminary data show that the TS preparation isolated from neonatal mice allows simultaneous recording of nerve terminal currents and post-synaptic events at end-plates receiving innervation from terminals originating in distinct nerve trunks. This allows unprecedented study of the function of, and NO-mediated cross talk between, mammalian nerve terminals competing for a postsynaptic target. The availability of epsilon subunit and nNOS knock out mice, as well as the epsilon AChR selective ligand Waglerin- 1 further strengthen experiments proposed to test our model. Additional novel preliminary data suggest that insulin, an activator of the neuronal K-ATP channel, suppresses quantal release of Ach at the adult NMJ. Therefore, a second goal of this proposal is to discover if insulin, as well as glucose, effects the function, and eventual stability, of nerve terminals competing at the developing NMJ. This will be explored in a non-obese mouse model of type I diabetes. Overall, this research is clinically relevant since NO signaling cascades are significantly altered in Duchenne muscular dystrophy as well as animal models of stroke. In addition, altered function of the epsilon AChR is responsible for NMJ pathology associated with slow channel congenital myasthenic syndrome. The proposed evaluation of insulin effects is novel and will enhance understanding of the neurologic consequence of adult and juvenile forms of diabetes. The knowledge gained from this research will enlighten future molecular approaches to treating pathologies which afflict children and adults.